In recent years, it is required for display devices used in portable devices, such as a smartphone and a tablet PC, to have high definition, for example, a pixel density of 400 ppi or higher. In addition, there is an increasing demand for adapting to ultra full high vision even with respect to the portable devices. In this case, it is required for the display devices to have a pixel density of, for example, 800 ppi or higher.
Among the display devices, an organic EL display device has drawn attention due to good responsiveness, low power consumption, and high contrast. As a method of forming pixels of the organic EL display device, a method of forming pixels in a desired pattern using a deposition mask having through-holes arranged in a desired pattern is known. Specifically, first, the deposition mask is brought into close contact with an organic EL substrate (deposition target substrate) for the organic EL display device, and then, a deposition step of introducing both the deposition mask and the organic EL substrate, in close contact with each other, into the deposition device to cause an organic material to be deposited on the organic EL substrate. In this case, it is required to precisely reproduce a position and a shape of the through-hole of the deposition mask in accordance with a design and to reduce a thickness of the deposition mask in order to precisely prepare the organic EL display device having a high pixel density.
As a method of manufacturing the deposition mask, a method of forming a through-hole in a metal plate by etching using a photolithography technique is known, for example, as disclosed in Patent Document 1. For example, a first resist pattern is first formed on a first surface of the metal plate, and a second resist pattern is formed on a second surface of the metal plate. Next, a region of the first surface of the metal plate that is not covered with the first resist pattern is etched to form a first opening on the first surface of the metal plate. Thereafter, a region of the second surface of the metal plate that is not covered with the second resist pattern is etched to form a second opening on the second surface of the metal plate. At this time, it is possible to form the through-hole penetrating the metal plate by performing etching such that the first opening and the second opening communicate with each other.
In addition, as the method of manufacturing the deposition mask, a method of manufacturing a deposition mask using a plating process is known, for example, as disclosed in Patent Document 2. For example, a base material having conductivity is produced first in the method described in Patent Document 2. Next, a resist pattern is formed on the base material with a predetermined gap therebetween. This resist pattern is provided at positions where through-holes of the deposition mask need to be formed. Thereafter, a plating solution is supplied to the gap of the resist pattern to precipitate a metal layer on the base material by an electrolytic plating process. Thereafter, the deposition mask having the plurality of through-holes formed therein can be obtained by separating the metal layer from the base material.    Patent Document 1: JP 5382259 B2    Patent Document 2: JP 2001-234385 A